1. Field of the Invention
The present invention relates to a light-emitting device, an optical module, and a fiber stub.
2. Description of Related Art
A light-emitting module is widely used for generating signal light to be input to an optical fiber that constitutes an optical transmission line in an optical communication system. The light-emitting module generally has a semiconductor laser device that generates a light signal and an optical system that includes a lens for directing the signal light to the optical fiber. A Fabry-Perot type semiconductor device or a DFB-type semiconductor laser device is used as the semiconductor laser device. Also, there is a light-emitting module in which an external cavity semiconductor laser system is used. In the external cavity semiconductor laser system, an optical cavity is composed of a semiconductor optical device and a Bragg grating.
The examples of a light-emitting device having an external cavity semiconductor laser system are described in Literature 1 (“Electronics Letters 20 Jun. 1991 vol.27 No.13, pp.1115-1116”), Literature 2 (Japanese Patent Application Publication Toku-kai-hei No. 6-5961), Literature 3 (WO 94/22187), and Literature 4 (Japanese Patent Application Publication No. 2000-353845), for example.
In particular, the light-emitting device described in Literature 1 is provided with a grating fiber part and a semiconductor optical device. The grating fiber part has an attachable/detachable connector through which it is connected to a package. With this composition, a light-emitting device for generating light with different wavelengths can be obtained easily. First, several kinds of grating fiber parts provided with diffraction gratings for different reflection wavelengths are prepared beforehand. A grating fiber part for a desired reflection wavelength is selected from them, and is attached to a package. Thus, the optical module emits light with the desired wavelength.
However, since the above-mentioned grating fiber part needs some length, it is often that the handling thereof is cumbersome. In particular, since a region for storing a grating fiber part is necessary, an optical transmitter device using such light-emitting device has a drawback that it is difficult to downsize. Also, according to the knowledge of the present inventor, a package of the type described in the above-mentioned literature is not preferable for downsizing an optical transmitter device because it tends to be large-sized. Moreover, there is a shortage that the productivity thereof is low in mass production, since a diffraction grating is formed one by one in each optical fiber having a given length.
Also, Literature 2 discloses an optical module in which an external cavity semiconductor laser system is used. In this optical module, a pigtail fiber extends in some length from the package of the optical module. When these light-emitting devices are mounted onto a circuit board, the pigtail fiber is rolled up and put on the circuit board. That is, it is necessary to provide the circuit board with a region on which the rolled pigtail fiber is put. In an optical communication system such as LAN (Local Area Network), for example, it is important to downsize a circuit board and it is preferable in such a field to decrease the above-mentioned region for disposing the pigtail fiber.